Existing marine propulsion systems typically utilize propellers (e.g., in the case of outboards, inboards, sterndrives, and pod drives) or impellers (e.g., in the case of jet drives) which rotate in a direction generally perpendicular to the surface of the water (or keel of the vessel). In other words, the rotation axes of known propellers or impellers extend along a direction generally parallel to the surface of the water. These systems may have certain drawbacks, including high drag levels due to excessive equipment surface below the waterline, high levels of cavitation due to the inefficiency of the direction of rotation in comparison to the direction of water flow, safety related issues due to rotating blades exposed in open water, and/or the like.
Many conventional marine propulsion systems also include a direct connection between the engine or motor and the drive unit, thereby locking the propeller speed directly in relation to the input speed. This reduces the efficiency of the system under certain conditions.